While apparatus and methods have been proposed in the prior art for cleaning pneumatic pressure operated spray guns, whether for paint or other liquid materials, a hitherto unsolved need has arisen for a more effective cleaning apparatus which is simple, yet effective in minimizing discharge of unwanted, and often very toxic or dangerous chemicals into the ambient environment at the clean up area.
For example, the Constantino U.S. Pat. No. 2,569,125 described a cleaning device for spray gun nozzles. The device essentially comprised three parts: a main reservoir tank, an auxiliary tank formed at one end of the main reservoir tank, and a hood or shroud portion over the main reservoir tank. A spray gun had its nozzle end inserted into a hole at the auxiliary tank end of the hood and had its suction tube inserted into the auxiliary tank which was filled with a suitable cleaning solvent. Then, air under pressure was flowed through the nozzle and sucked up cleaning fluid by operation of a venturi between the suction tube and a main airflow line leading to the nozzle. The droplets of cleaning fluid were said to be condensed and collected on the inside walls of the shroud and thereupon be returned by gravity flow into the main reservoir tank.
U.S. Pat. Nos. 4,460,126 and 4,534,802 to Gates et al., and U.S. Pat. No. 4,204,977 to Zwirlein disclose apparatus and methods directed to purging polyurethane foam spray gun apparatus. In Zwirlein, for example, positive pressure is provided through the gun to circulate solvent during periods of non-use in order to prevent any urethane foam within the gun and its nozzle from hardening. Complex pumping apparatus was required in order to carry out the necessary recirculation during periods of non use of the gun.
U.S. Pat. No. 3,876,114 to Hicks et al, describes a cleaning apparatus for a hand held dispensing gun of the type used for dispensing synthetic resin liquid material. The air powered flush system first injected a small quantity of solvent into the mixing chamber of the gun, the then followed with a high pressure air blast which atomized the solvent and caused it to flush out all of the resin that might have remained in the mixing chamber within the gun.
U.S. Pat. No. 3,240,225 to Barrows describes a turreted assembly for automatically connecting a wide variety of paint sources (typically holding different colored paints) to a single spray gun. This special apparatus included a purging cycle to purge the nozzle of the last used paint before the next used paint entered the gun. The application described for this special apparatus was assembly line painting of automobiles. Furthermore, in European Patent Application No. E.P. 230,245 published July 29, 1987, of L. E. Stern et al, another cleaning device for spray guns is described. It comprises a suction system that generates a suction through a connecting element attached to the nozzle of the spray gun. With the suction system activated, cleaning solvent is sucked from the paint supply reservoir (can) portion of the gun through its discharge nozzle, directly into a confined filter, and thence to one or more waste collecting containers. The gun itself is neither connected to an independent source of compressed air nor is the trigger of the gun activated during cleaning. As a result the suction system must be positioned closely adjacent to the spray gun to maximize suction since the flow of the solvent/paint mixture from the spray gun is only a function of the relative low pressure generated by the suction system. Also there is not enough space to provide an enclosed path for the removed cleaning fluid and other toxic material. Instead, such fluid material must flow from a separation means (of a suitable filter material) into a large open washing bowl and thence to the waste container. But when the associated vapors are in the open bowl, they are directly exhausted to the ambient atmosphere. Further, the suction system employs a "Coanda Effect" to produce the suction, and the suction is split between drawing on the gun and on a small vapor hood over the open solvent bowl. The solvent bowl vapors are ejected directly to the atmosphere without filtration, condensation or collection.
None of the foregoing examples of the state of the art provide a very simple and low cost, yet highly effective cleaning apparatus for a point spray gun of the type commonly employed in automobile body repair shops throughout the world. In automobile body repair shops, while a paint spray booth may have been provided, the problem of free droplets of paint condensing onto adjacent vehicles being worked on created needless problems and required additional time to correct. Also, there has been a growing concern for not polluting the environment with toxic materials including spray paint and the like. The present invention addresses and solves these problems.